Air Force Staff Sgt. Luis Walker arrives for the fourth day of his trial Friday at Lackland Air Force Base in San Antonio, Texas. Walker is accused of sexually assaulting 10 basic trainees, with charges ranging from rape and aggravated sexual assault to obstructing justice and violating rules of professional conduct. (ASSOCIATED PRESS / San Antonio Express News, Billy Calzada)

SAN ANTONIO (AP) — An Air Force instructor implicated in a sweeping sex scandal at one of the nation’s busiest military training bases was convicted in military court Friday of raping one female recruit and sexually assaulting several others.

Staff Sgt. Luis Walker, the first Lackland Air Force Base instructor to stand trial in the scandal, was found guilty by a jury of seven military personnel on all 28 counts he faced, including rape, aggravated sexual contact and multiple counts of aggravated sexual assault.

The jury deleted a clause from two counts that accused Walker of making flirtatious and lewd comments to trainees. However, it upheld the overall counts containing the deleted clauses, which accused him of trying to cultivate a sexual relationship with two trainees.

Walker faces up to life in prison and a dishonorable discharge at his sentencing hearing, which starts Saturday. He showed no emotion upon hearing the verdict. Outside the base courtroom afterward, Walker was met by his father and other relatives, some of whom were crying. He will remain free pending sentencing.

Walker is among 12 Lackland instructors investigated for sexual misconduct toward at least 31 female trainees. Six instructors have been charged on counts ranging from rape to adultery. Walker faced the most serious charges and was the first to stand trial.

Lackland is where every American airman receives basic training. It has about 475 instructors for the approximately 35,000 airmen who graduate every year. About one in five is female, pushed through eight weeks of basic training by a group of instructors, 90 percent of whom are men.

The sexual misconduct at the base apparently began in 2009, but the first woman didn’t come forward until last year. The first allegations were levied against Walker, who is accused of crimes that allegedly took place between October 2010 and January 2011.

According to prosecutors, Walker had sexual intercourse with 4 of the 10 female recruits. He was also accused of making flirtatious or sexually suggestive comments, sending inappropriate text messages and sometimes groping his recruits.

Walker also is accused of forcing five recruits to engage in sexual acts by threatening their military careers and intimidating two of the women into lying about his alleged misconduct, prosecutors alleged.

Several of Walker’s alleged victims testified during his court-martial, including one airman who described how Walker lured her into an office and sexually assaulted her on a bed, ignoring her pleas to stop.

The women told jurors that Walker gained their trust to get them alone in his office or an empty dormitory where he forced them into kissing, touching and intercourse. Those testifying said they didn’t tell anybody at first because they feared being booted from the Air Force.

The Associated Press is not naming those who testified because they are alleged sexual assault victims.

Meanwhile, the case of another former Air Force training instructor has been referred to a general court-martial, according to an Air Force statement issued Friday evening.

Staff Sgt. Craig LeBlanc is charged with sexual misconduct, obstructing justice and making a false official statement. He is accused of using his post as a military instructor to sexually assault and pursue a sexual relationship with one female trainee, and have a wrongful sexual relationship with another. No trial date has been set.

One of the other instructors charged in the case, Staff Sgt. Peter Vega-Maldonado, pleaded guilty in June, admitting he had sex with a female trainee in exchange for a sentence of 90 days’ confinement. He later acknowledged he had been involved with a total of 10 trainees — a number previously unknown to investigators.